1. Field of the Invention
The present invention relates to an image processing device, an image processing method, and a non-transitory computer readable recording medium storing a program that compare a radiation image of a test object with a standard image.
2. Description of the Related Art
As a method for testing defects of various test objects such as industrial parts (products) or industrial facilities, a non-destructive testing (NDT) technique using radiation such as X-rays is known.
In such non-destructive testing technique, radiation such as X-rays is emitted to a test object, the radiation that transmitted the test object is imaged by an imaging unit, a radiation transmission image obtained by the imaging is displayed on a display unit, and an inspector observes a difference between display (digital) driving level (DDL) values of the displayed radiation transmission image to determine the presence or absence of a defect in the test object. Here, in a case in which the test object has a three-dimensionally complicated shape, it is difficult to distinguish original convex and concave of the test object from defects thereof. Further, there is a case where it is difficult to for an inspector recognize a fine difference between the DDL values due to a sensitivity difference which is a difference between ranges where respective inspectors can recognize the fine difference between the DDL values. As a result, it is difficult to directly specify a defect of a test object from a radiation transmission image.
JP2012-088291A and JP1991-137548A (JP-H03-137548A) disclose a method for determining the presence or absence of a defect of a test object on the basis of a differential image between a radiation transmission image obtained by imaging radiation that transmitted a test object and a standard image obtained by imaging radiation that transmitted a normal test object with no defect.
JP1996-146137A (JP-H08-146137A) discloses a method for obtaining a differential image between two radiation transmission images obtained by imaging radiation that transmitted a test object at different timings while relatively moving one of the test object and an imaging unit to the other, and detecting a defect image in the test object on the differential image as a double image.
JP4988482B discloses a method for detecting the presence or absence of a defect of a test object on the basis of an image obtained by offset-correcting a radiation image obtained by imaging radiation that transmitted the test object using correction image data. In JP4988482B, differential image data between a radiation image obtained by imaging radiation that transmitted an object having a uniform thickness larger than of the test object and an average image of a plurality of radiation images obtained by imaging radiation that respectively transmitted a plurality of test objects is used as the correction image data.
JP1991-209583A (JP-H03-209583A) discloses a method for removing influences other than a defect by, for example, a quadratic curve approximating process from a radiation image obtained by imaging radiation that transmitted a test object to obtain an image in which the defect is emphasized, thereby detecting the defect of the test object.